K-Patents PR-33-S - Manual (Page 6)

2 PR-33-S instruction manual
Document/Revision No. Rev. 1.4 Effective: May 15, 2015
L
P
M M
S
A C B
Figure 1.2 Refractometer principle
The refractive index n
D
changes with the process solution concentration and temper-
ature. For most solutions the refractive index increases when the concentration in-
creases. At higher temperatures the refractive index is smaller than at lower tempera-
tures. From this follows that the optical image changes with the process solution con-
centration as shown in Figure 1.3. The color of the solution, gas bubbles or undissolved
particles do not affect the position of the shadow edge (C).
B B C C A A
Low concentration High concentration
Figure 1.3 Optical images
The position of the shadow edge is measured digitally using a CCD element (Figure 1.4)
and is converted to a refractive index value n
D
by a processor inside the instrument.
This value is used together with the measured process temperature to calculate the
concentration.